This invention relates to a failure diagnosis technology for diagnosing a failure occurring in a photovoltaic system including a large number of photovoltaic modules.
A large-scale photovoltaic system as represented by a mega solar system includes several thousands to hundreds of thousands of 100-watt to 200-watt class photovoltaic modules arranged in one power generation site and requires failure detection technologies and maintenance technologies. An output of each of the photovoltaic modules gradually decreases under the same irradiation and temperature conditions due to degradation over time. However, the outputs of some modules suddenly drop due to manufacturing quality or physical damage. A state in which the output suddenly drops is referred to as “failure”.
Output characteristics of the photovoltaic system considerably vary depending on environmental conditions such as the irradiation. Therefore, even in the case where its normal output is not obtained due to a failure or degradation of the photovoltaic modules constructing a photovoltaic panel, it is difficult to distinguish the output drop due to the failure or degradation from that under the effects of the environmental conditions. As a method of detecting the failure of the photovoltaic module, a visual inspection, a heat-generation inspection using a thermometer, and an electrical characteristic inspection using a tester have been conducted. However, the above-mentioned inspections are conducted for each of the photovoltaic modules. Therefore, there is a problem in that, for the mega solar system which includes hundreds of thousands of photovoltaic modules, the efforts and costs required for the inspection are disadvantageously increased.
To cope with the problem described above, the following method is disclosed in JP 2010-123880 A. According to the method, measurement means and communication means are provided for each of the photovoltaic modules. In order to automatically determine whether or not a failure occurs in the photovoltaic module, the result of measurement transmitted from the communication means and a threshold value are compared with each other.
JP 2010-123880 A discloses the method in which the measurement means and the communication means are provided for each of the photovoltaic modules. The measurement means and the communication means, which are to be mounted to each of the photovoltaic modules, additionally require means for installing the measurement means and the communication means. The means for the installation is required to have a life span of 10 years to 20 years. Therefore, extremely high installation costs are required. Moreover, the output characteristics of the photovoltaic module considerably vary depending on the environmental conditions such as the irradiation. Thus, it has hitherto been difficult to set a threshold value for determining the output drop of the photovoltaic module due to a failure or degradation.